1. Field of the Invention
The invention relates to thin films of magnetically soft alloys. More particularly, the invention relates to articles comprising these alloys.
2. Description of the Related Art
Soft magnetic thin films are useful in modern, high-frequency, electromagnetic devices as a field-amplifying component, e.g., in the read-write head for magnetic disk memories in computers or as a core in microtransformers and inductors. Among the desired properties of these films are relatively high saturation magnetization (4.pi.M.sub.s), low coercivity (H.sub.c), high permeability, high electrical resistivity and corrosion resistance. Various applications of soft magnetic thin films are described, for example, in books Magnetic Thin Films by R. F. Soohoo, Harper and Row, 1965; Thin Ferromagnetic Films by M. Prutton, Butterworth, 1964; and in articles C. R. Sullivan and S. R. Sanders, IEEE Trans. on Power Electronics, Proc. 24th Annual Power Electronics Specialists Conf., p. 33-40, June 1993; and T. Yachi et al., IEEE Trans. Magn. 28, 1969-1973 (1992).
Among the known soft magnetic thin films, nickel--iron (Ni--Fe) based films such as 80% Ni-20% Fe (permalloy) are used most widely because of excellent magnetic properties and zero magnetostriction characteristics. Fe-based films such as iron--tantalum (Fe--Ta), iron--zirconium (Fe--Zr) and iron--hafnium (Fe--Hf) alloys generally exhibit higher saturation magnetization of 15-20 kilogauss (kG) as compared to about 10 kG for the 80% Ni permalloy films (see, e.g., N. Kataoka et al., Japanese J. Appl. Phys. 28, L462-L464, 1989, Trans. Jap. Inst. Metals 31, 429, 1990), however, they exhibit poorer soft magnetic properties and require post-deposition heat treatment.
To obtain improved soft magnetic properties, nitrogen-containing films of these Fe-based alloys such as iron--tantalum--nitrogen (Fe--Ta--N) have been prepared. See, for example, E. Haftek et al., IEEE Trans. Magn. 30, 3915-3917 (1994); N. Ishiwata et al., J. Appl. Phys. 69, 5616 (1991); J. Lin et al., IEEE Trans. Magn. 30, 3912-3914 (1994); and G. Qiu et al., J. Appl. Phys. 73, 6573 (1993). However, although desirable magnetic softness with a coercivity, H.sub.c, of less than approximately 2 oersted (Oe), which is desirable for microtransformer applications, is obtainable in these nitrogen-containing films, it is apparent from the aforementioned articles that such desirable soft magnetic properties are difficult to obtain in the as-deposited films, but are possible after post-deposition heat treatment at high temperatures.
However, such heat treatment of deposited films is an additional processing step that needs to be avoided if possible, not only from the manufacturing cost point of view but also because of the complications of having to expose to high temperature various other components and materials in the devices. As a result of high temperature exposure, some of these components can be damaged, e.g., decomposition of polymers or polyimide insulating films, diffusion-induced chemical changes or damages, stress problems caused by thermal expansion mismatch of different materials.
Therefore, it is desirable for the required soft magnetic properties in the films to be obtained in the as-deposited condition, or at the worst, with a very low temperature heat treatment below approximately 150.degree. C. where damage to polymers such as polyimide is kept relatively low. This application discloses new soft magnetic films with such desirable characteristics. Also, it is desirable to improve the corrosion/oxidation resistance of the Fe-rich thin films, as the oxides of iron and iron-rich alloys generally exhibit substantially reduced magnetic saturation. This application discloses thin films with improved corrosion resistance.